Participants with SAD will be interviewed periodically on an outpatient basis to determine the onset of depression in the fall or winter. Two weeks after depressive symptoms arise, participants will begin treatment with either propranolol or placebo. At the beginning of the treatment, participants will be hospitalized for about 2 days and will have blood collected at various times. During the hospital stay, participants will continue treatment with either propranolol or placebo in the morning and at night; all participants will receive propranolol at some point during the study. Participants will be interviewed weekly for 4 weeks.